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Sigma - Globals do not work when an IP Address structure of 192.168.xxx.xxx Mask 255.255.0.0 is used.

Issue

Sigma globals do not work.

Environment

Sigma

Globals

Mask 255.255.0.0

Classful

Classless

Cause

The site is using a class C address, with a class B subnet mask.

Resolution

The following is an explanation of why the Sigma globals in this configuration do not work.

An IP Address is divided in to two sections: Net ID and Host ID. The Host ID is further divided in to two Sections: Subnet ID and Host ID.

  • The Subnet Mask determines the Subnet ID bits and Host ID bits.
  • Number of Mask bits should be greater than that of Net ID bits.

For example a Sigma address is 192.168.0.1 with 24 bit mask 255.255.255.0

  • Number of subnet ID bits is zero and Host ID bits is 8;
  • Broadcast address is 192.168.0.255

 With 28 bit mask 255.255.255.240

  • Number of subnet ID bits is 4 and Host ID bits is 4;
  • Broadcast address is 192.168.0.15

 For Class C:

  • Address range is: 192.0.0.0 to 223.255.255.255 inclusive
  • Net ID is 24 bits; Host id is 8 bits; Minimum Mask size is 24 bits;

 For Class B:

  • Address range is: 128.0.0.0 to 191.255.255.255 inclusive
  • Net ID is 16 bits; Host id is 16 bits; Minimum Mask size is 16 bits;

In the site set up, 192.168.xxx.xxx is a Class C address; this can have at least 24 bit mask; 16 bit mask is invalid;

Using an Address 190.168.xxx.xxx works correctly because it is a Class B address and supports 16 bit masking; hence works properly.

For globals to work correctly, either use >= 24 bit mask for the subnet 192.168.xxx.xxx, or move to class B subnet 190.168.xxx.xxx.

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Last update:
‎2018-09-06 12:39 PM
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